Elliptically polarized spiral antenna



Jan. 30, 1962 H. J. REIS ETAL 3,019,439

ELLIPTICALLY POLARIZED SPIRAL ANTENNA Filed Sept. 19, 1957 4Sheets-Sheet 2 INVENTOR. HERBERT J. REIS FRANCIS M. KUDO AT TORNEY Jan.30, 1962 H. J. REIS ETAL 3,019,439

ELLIPTICALLY POLARIZED SPIRAL ANTENNA Filed Sept. 19, 1957 4SheecS-Sheel'I I5 INVENTOR. HERBERT J. REIS FRANCIS M. KUDO ATTORNEY H.J. REIS ETAL ELLIPTICALLY POLARIZED SPIRAL ANTENNA Jan. 30, 1962 4Sheets-Sheet 4 Filed Sept. 19, 1957 3,019,439 ELLIITICALLY POLARIZEDSPIRAL ANTENNA Herbert J. Reis, Middle River, and Francis M. Kudo,Kenwood, Md., assigncrs to Martin-Marietta Corporation, a corporation ofMaryland Filed Sept. 19, 1957, Ser. No. 684,876 19 Claims. (Cl. S45-853)This invention relates to an antenna of generally spiral construction,iiush mounted with the surface of a ground Waves in an eiiicient mannerand over a wide range of frequencies.

e past, so-called stub In th with a moderate degree of success forcommunication and for only of an octave.

drag. Other advantages.

According to the a novel and improved travelling wave antenna which, be

both the horizontal and vertical planes, for use in electroniccountermeasures equipment and ground based weapons systems.

The antenna is small,

the radiating elements are in the form of interwound spirals formedabout a common axis and located in a substantially common plane, withbalanced feed means connected to the radially inner ends of the elementswhereby a balin a number of locations in the process of winding acrossthe face of the antenna. As a further modification, the central portionof the face of the antenna may be raised somewhat, this having theresult of producing radiation closeito the ground plane rather than inmodifications not having the raised central wound spirals formed aboutportion. Spiral radiating elements may be employed in the modificationhaving the raised central portion, as may radiating elements ofessentially square configuration previously described.

Since the mean diameter of the radiating circumferential zone varieswith frequency, a broad frequency range of operation is possible with anantenna of suitable diameter. Because of the orientation anddistrbiution of field vectors, a null is produced in a direction normalto the plane of the antenna, with consequent radiation extending in alateral, encircling direction above (or below) the ground plane of theantenna. Due to the many windings of the antenna, a traveling waveexists along the turns to yield omnia'zimuthal radiation along a widefrequency range.

The above and other features in this invention will become apparent uponreference to thefolllowing detailed description and accompanyingdrawings in which:

FIGURE 1 is a plan View of a first embodiment of a multi-conductorspiral antenna according to this invention;

FIGURE 2 is a side View of the antenna according to FIGURE l, partly insection to reveal internal construction;

FIGURE 3 is a simplified view revealing details of the feed means andthe polarities associated with the coaxial conductors employed in theantenna according to this modification;

FIGURE 4 is an exploded lview of the antenna according to FIGURES 1 and2 revealing inner construction;

FIGURE 5 is a simplified diagram of the .radiating elements of theantenna of FIGURES 1 and 2, revealing direction of current flow throughthe radiating elements at a given instant and the direction of thegenerated electric field in the circumferential region from whichradiation originates;

FIGURE 6 is a typical conical radiation pattern of the type obtained bythe use of an antenna of the type shown in FIGURES l and 2;

FIGURE 7 is a view taken through the radiation pattern of FIGURE 6,revealing the manner in which a given section of the radiation patternis polarized according to components at one instant;

FIGURE 8 is a plan view of a second embodiment according to thisinvention in which the radiating elements are of substantially squareconfiguration;

FIGURE 9 is a plan view of a third embodiment of this invention in whichthe radiating elements are similar to those of the second embodiment,but with the central portion of the antenna raised;

FIGURE 10 is a perspective view of the antenna according to FIGURE 9;

FIGURE 1l is a simplified view similar to FIGURE 3 revealing how thefeed means are connected to the radiat ing elements of an antenna inwhich the central portion is raised;

FIGURE l2 is a conical radiation pattern similar to FIGURE 6, thispattern being obtained from an antenna having a raised central portion;and

FIGURE 13 is a view taken through the antenna pattern of FIGURE 12,revealing the components of po1arization of a given section thereof at agiven instant.

Referring initially to FIGURE 1, there is illustrated an antenna 10constituting a first embodiment of this invention wherein the radiatingportion or face 11 consists of radiating elements 12, 13, 14 and 15 inthe form of intera central axis and disposed in a common plane. Theinner ends of these elements terminate in a common central area at feedpoints 12', 13', 14 and 15 respectively. The outer ends of theseelements may terminate adjacent the outer edge of the` antenna in anyconvenient manner such as the 90 relationships shown.

The radiating elements are electrically isolated from each other, andaccordingly printed circuitry techniques may be employed in theillustrated embodiment for the creation of radiating elements upon adielectric sheet 16. The sheet 16 may be structurally mounted bysuitable screws or the like upon a mounting plate 17, which in turn maybe provided with mounting holes 13 to enable the. antenna to be, securedin the desired operating position, such as to the underside of anaircraft. Radiating elements of other construction may of course beemployed if desired.

In FIGURE 2 a cavity 21 is defined on the side of the dielectric sheetthat is remote from the radiatingI elements, and to this end, a cavityplate 19 is secured to the underside of mounting plate 17 in theillustrated manner. The cavity plate is provided with circumferentialedge portions 2'2 located radially outwardly of the radial portion ofthe antenna so as to define a closed cavity and to properly supportplate 19 with respect to mounting plate 17. If desired, members 17, 19and 22 can be of integral construction, such as by the employment ofmetal stamping techniques.

Although there is no definite size for cavity 21, the best results havebeen. obtained when the depth of this cavity is slightly less than aquarter wave length at the high frequency end of the band of operation.The cavity 21 acts as a reector to direct radiation outwardly from theface of the dielectric sheet in which the radiating elements aredisposed, for without the presence of the cavity, an antenna of thistype would tend to radiate energy both below and above the ground plane,thereby dissipating its power in an undesirable direction and decreasingits range and overall efficiency. Other details of this construction maybe observed by referring to FIG- URE 4.

Centrally mounted on the lower side of cavity plate 19 is a connector 38through the interior of which are located a plurality of coaxial linesfor supplying energy to the radiating elements. Inasmuch as fourradiating elements 12 through 15 are employed in this embodiment, thelines 32 through 35 are connected to these elements, respectively, atfeed points 12', 13', 14 and 15 aspreviously mentioned.

Since coaxial lines 32 -through 35 are to be connected to coaxial feedcable 23 in a balanced arrangement, a broad band balun 31 is preferablysecured to the lower end of connector 38. This type of balun isdescribed at some length by Nathan Marchand in his article entitled, f

Transmission-Line Conversion, in Electronics December 1944 issue, pages142 through 145. As brought out in the article, whenever it is necessaryto use a balanced two wire line over one part of a system and a coaxialtransmission line over another part of the system, a conversiontransformer is often necessary at the juncture of the two types of linesin order to maintain currents on the two types of lines in their properrelations.

In FIGURE 2, the balun 31 is generally of the type shown in Figure 6 ofthe Marchand article and employs a solid stub 29 centrally disposed inone end of the balun, and extending for approximately one half thelength thereof. Coaxial feed line 23 is attached to the opposite end ofthe balun, with outer conductor 25 being secured to the continuousshield forming the exterior of the balun, and the inner conductor 24being tapered to a size commensurate with the size of coaxial line 26located in the balun in aligned relationship with solid stub 29. Theinner'conductor 24 is connected to inner conductor 27 of line 26, andconductor 27 in turn is connected to solid stub 29 by a suitableelectrical connection. Outer conductor 28 of line 26 terminatesapproximately at the midpoint of the balun but spaced somewhat from thestub 29. Dielectric portion 36 of line 26 separates conductors 27 and28, continues past the termination of outer conductor 23 into contactwith stub 29, although dielectric 36 is apertured to receive a smallblock of dielectric 37 on its upper side. The dielectric 37 is insertedin this gap between conductor 2S and stub 29 so as to increase thedielectric strength of the medium in the gap, thereby increasing thepower handling capabilities of the balun.

The four coaxial lines 32 through 35 are connected in a particulararrangement as illustrated in FIGURES 2 and 3 so as to achieve abalanced arrangement. The center conductor of each lines 32 and 33 isconnected to the outer conductor 2% of coaxial line 26, and the centerconductors of lines 34 and 35 are connected to the solid stub 29.Balance is achieved by crossing over two of the lines as shown inFIGURES 2 and 3 so that polarities are attained for the antenna feedterminals as shown in FiGURES l and 3. In other words, when terminals 12and 14 are positive, terminals 13 and 15' will be negative and viceversa. Freferably the top and bottom ends of the outer conductors oflines 32 through 35 are connected to ground for shielding purposes, thisalso causing the capacity from center conductors to ground for all fourlines to be equal.

FIGURE 5 is illustrative associated with this antenna. 42 through. 45correspond with radiating elements 12 through 15 of FIGURE l.. Whenthese elements are energized in the manner indicated by the inner arrowsI, the current vectors I indicated by dotted lines will be establishedat radially outer locations on the radiating elements. Since eachradiating element is typically many wave lengths long and radiationoriginates in a mean circumferential region equaling two wave lengths,the direction of the arrows representing current in the radiating regionis approximately as shown. Electric field vectors E are produced in acircumferential zone with orientation similar to that shown in thisfigure, lying substantially at right angles to the current vectors I.Also, since the mean diameter of the radiating circumferential zonevaries with frequency, a broad range of operation is achieved by the useof an antenna of suitable diameter. Because of the orientation anddistribution of the eld vectors, a null is produced in a directionnormal to the plane of the spiral, with energy being radiated toward allsides.

FIGURE 6 is illustrative of the type of radiation pattern produced by anantenna as described. Elliptically polarized energy is radiated orreceived in all directions on the side of the ground plane upon whichthe antenna is mounted. FIGURE 7, which is a typical section takenthrough the radiation pattern of FIGURE 6, reveals the polarization oftwo components of the radiated electric field at any one instant. Moreparticularly, due to the current distribution at the antenna in thehorizontal plane as shown in FIGURE 5, horizontally polarized componentsof the radiating electric field are achieved in space. Two of thesecomponents are shown in FIGURE 7 by the vectors E, where the vector inthe left lobe is entering the plane of the page, whereas the othervector is coming out of the page in the right lobe, this correspondingwith the phasing of diametrically opposite current vectors at theantenna.

Due to the radial electric field distribution at the antenna as `shownin FIGURE 5, electric field radiation po, larized in the G-direction isalso achieved. In FIGURE 7, two 0 components of the electric field areshown by vectors E, which point downwardly at a slant anglecorresponding to the 0-direction, this also corresponding with theelectric field vectors pointing outwardly in FIGURE 5. This polarizationbears a resemblance to that obtained from radiation by an annular slotantenna in a finite ground plane where the electric field at the antennais also radial. As a result of the radial electric field at the antenna,the polarization of the radiated field from the annular slot antenna isalso in the 0-direction.

A spiral type antenna as described herein differs from of the theory ofoperation The four radiating elements the annular slot, loop, and otherresonant antennas wherein standing waves exist, for the spiral typeantenna contains traveling waves along the radiating elements. Becauseof the configuration of the antenna, and more speciiically the fourconductors, spacing between conductors, many turns, and polarities ofthe feed terminals, the current and electric field distributions shownin FIGURE are achieved in a region corresponding to a mean circumferenceof two wave lengths, this accounting for the orientations of the currentand electric field vectors illustrated in the latter figure. Sincetraveling waves exist in the antenna, nearly equal radiation is achievedalong circles parallel to the face of the spiral with centers along theperpendicular axis of the spiral. Elliptical polarization is obtainedbecause the Eg, and E, components are about 90 out of time phase.

Referring to FIGURE 8, another embodiment according to this invention isshown, with the radiating elements through 55 corresponding to elements12 through 15 and 42 through 45 of earlier figures, and preferably being8 form 'an figuration, `with each element being bent approximately 90 Data number of locations in the process of winding across the face of theantenna. Feed points 52 and 54 of elements 52 and 54 are connected tothe outer conductor of a coaxial line, and feed point 53 is connected tothe center conductor. Although a balun is not used in the illustratedembodiment, a shallow cavity (not shown) is mounted on the underside ofthe antenna in a manner similar to that shown in FlGURE 2. The cavity issquare to conform to the square configuration of the radiator, but it`can be circular if desired. A feed arrangement can consist olf a singlecoaxial line passed through the bottom center of the cavity andelectrically connected to the radiating elements in the aforementionedmanner.

A study of feed points shows that current distribution at the center ofthis antenna embodiment is similar to that shown in FiGURE 5 since, whencurrent is lowing toward 53' in conductors 53 and 55, current will owaway from 5,2 and 54 because these points are of opposite polarity withrespect to that of feed point 53. Current and electric fielddistributions in the circumferential radiating zones are similar to thatachieved in the embodiment shown in FIGURE l, because of the similarcurrent distribution at the center and the generally spiral typeconfiguration of the radiator. However, due to the unbalanced feedarrangement sbown in FIGURE 8, radiation in yazimuth is notassymmetrical as that obtained from the antenna shown in FIGURE l, whereina balun was employed. If the balanced feed arrangement be indicated, abalun may of course be employed with the antenna illustrated in FIGURE8.

Referring now to FIGURES 9 and l0, an embodiment is illustrated in whichthe central portion of the face of the antenna is raised to form asomewhat pyramidal configuration. However, as an example, the centralportion of the face of the antenna may be raised in the order ofmagnitude of 5/8, so that the radiating elements 62 through 65 of thisembodiment are still disposed in a substantially common plane upondielectric sheet 66. Therefore the increase, if any, in aerodynamic dragof this embodiment when employed in an aircraft is small. Although thedesired type of feeding arrangement may off course be employed with thisembodiment as with the earlier embodiments, a balun is preferably used,With the feed lines preferably being crossed as shown in FIGURE ll inorder that balance will be achieved. In the latter figure, cavity 71 isdefined by a tapered bottom surface that agrees fairly closely with theconfiguration of the radiating surface of the antenna.

Since the mean diameter of the radiating circumferential zone variesinversely with frequency, radiation at the high frequency end of theoperating band originates near the apex of the pyramid to produceradiation closer to the ground plane than radiation from a fiat spiralantenna. However, the reduction in angle of radiation at the lowfrequency end of the operating band is not as significant becauseradiation originates near the base of the pyramid where the diameter ofthe pyramid is greater.

The radiation patterns obtained by the use of the embodiment accordingto FIGURES 9 and l() are shown in EIGURES 12 and 13, which correspondcomparatively closely with the radiation pattern illustrated in FIGURES6 and 7 but with the radiation being somewhat closer to the ground planebecause of the raised central portion of the antenna.

The described embodiments of an antenna according to this invention aremerely exemplary, and other configurations and other feedingarrangements are possible within the orbit of this invention. As anexample, the balun could be eliminated and a balanced arrangementnevertheless obtained if separate generators are used to energize Itheradiating elements, the generators being phased so as to presentappropriate polarities. By the selection of the desired configuration,various radiation patterns may be obtained which advantageously areelliptically polarized and designed vfor operation over a wide frequencyrange.

We claim:

l. A flush mounted elliptically polarized omniazimuthal antenna having aface, and a plurality of at least four conducting elements electricallyisolated from each other and interwound in a common direction acrosssaid face so that the introduction of electromagnetic energy to saidantenna will produce apparent current vectors at quadratic points aroundthe means circumferential region of said elements, the apparent currentvector at any one quadratic point being circumferentially opposed to theapparent current vectors at the adjacent quadratic points, whereby saidantenna will have an elliptically polarized omniazimuthal pattern.

2. A iiush mounted elliptically polarized omniazimuthal antenna having aface and an underside, a plurality of at least four conducting elementselectrically isolated from each other and interwound in a commondirection across said face so that introduction of electromagneticenergy to said antenna Will produce apparent current vectors atquadratic points around the mean circumferential region of saidelements, the apparent current vector at any one quadratic point beingcircumferentially opposed to the apparent current vector of the adjacentquadratic points, balanced coupling means mounted on said underside,with the radially inner ends of said radiating elements connected tosaid coupling means, whereby a balanced and symmetrical wave pattern maybe transmitted.

3. The antenna as defined in claim 2 in which mounting means for saidantenna are provided, said mounting means deiining a cavity on theunderside of said antenna of a depth approximately 1A wave length,whereby a radiation pattern is principally formed on the face side ofsaid antenna.

4. A liush mounted elliptically polarized omniazimuthal antenna ofgenerally spiral construction having a face, a plurality of at leastfour conducting elements interwound about a common axis in the samedirection across a portion of said face, said conducting elements beingelectrically isolated from each other and disposed substantially in acommon plane, and balanced feed means connected to the radially innerends of said elements so that when energy is coupled into said antennathrough introduction of electromagnetic energy apparent current vectorswill be produced at quadratic points around the mean circumferentialregion of said elements, the apparent current vector at any onequadratic point being circumferentially opposed to the apparent currentvector at the quadratic points adjacent thereto, whereby a balanced landsymmetrical wave pattern may be transmitted by said antenna.

5. The antenna as defined in claim 4 in which said conducting elementsare in the form of interwound spirals.

ama/teo 6. The antenna as defined in claim 4 in which said conductingelements form an essentially square contiguration, with each elementbeing bent approximately 90 in a number of locations on the face of theantenna.

7. The antenna as defined in claim 4 in which a central portion of saidface is slightly raised, with said fee-d means connected at said raisedportion to the inner ends of said eiements.

8. The antenna as defined in claim 4 in which said conducting elementsare disposed upon dielectric material, and said feed means includes ahalun connected to said elements by means of a plurality of balancedoutput conductors connected in an electrically symmetrical arrangement.

9. An elliptically polarized omniazimuthal antenna adapted to be flushmounted on the surface of an aircraft or the like comprising a pluralityof at least four interwound conducting elements disposed in a generallyspiral arrangement upon dielectric material, mounting means for saidantenna including means deiining a cavity of a depth of approximately 1Aof a wave length on the side of the antenna opposite the surface of saidelements, and feed means including a balun for energizing said elementsso that the introduction of electromagnetic energy to said antenna willproduce apparent current vectors at quadratic points around the meancircumferential region of said elements, the apparent current vector atany one quadratic point being opposed in a circumferential direction tothe apparent current vectors at the quadratic points adjacent thereto,and a plurality of balanced output conductors connecting said elementswith said balun in an electrically symmetrical arrangement.

10. The antenna as deiined in claim 9 in which said conducting elementseach are formed with a number of 90 bends so that said elements define asubstantially square configuration on the face of said antenna.

11. The antenna as defined in claim 9 in which the central portion ofsaid antenna is raised somewhat so as to cause the radiation pattern ofthe antenna to occur closer to :the ground plane of the antenna.

12. An antenna mounted flush with the surface of a ground plane fortransmitting and receiving electromagnetic energy in an elliptica/llypolarized pattern comprising ya face, and four radiating elementsinterwound about a common axis in the same direction across a portion ofsaid face,y said radiating elements being electrically isolated fromeach other and disposed substantially in a common plane, and couplingmeans connected to the first and third of said four conducting elementsin afirst phase relation and connected to the second and fourth of saidelements in a second phase relation displaced substantially 180electrical degrees from said first phase relation, whereby inunder forconcentrating S troduction of electromagnetic energy to said antennawill produce apparent current vectors at quadratic points around themean circumferential region of said elements, the apparent currentvector at any one quadratic point being circumferentially opposed to theapparent current vectors at the quadratic points adjacent thereto.

13. The antenna as deiined in claim 12 in which said radiating elementsare disposed upon dielectric material.

14. The antenna as defined in claim 12 in which said radiating elementsare in the form of intertvound spirals.

15. The antenna 'as defined in claim 12- in which said radiatingelements -torm an essentially square coniiguration, with each elementbeing bent approximately 90 in a number of locations on the face of theantenna.

16. The antenna as defined in claim 12 in which a eentral portion ofsaid face is slightly raised, with said feed means connected at saidraised portion to the inner ends of said elements.

17. An antenna in accordance With claim 12 in which I said couplingmeans is a two-wire transmission line.

1S. An antenna in accordance with claim 12 which includes means formatching impedances between said coupling means and the ultizationcircuitry, and mounting means on the underside of said face defining acavity therethe radiation pattern of said antenna on the other sideofsaid face.

19. An antenna in accordance with claim 18 in which said means formatchingr impedances is a` balun, and the said first and third elementsare electrically shorted, and the said second and fourth elements areelectrically snorted together, said coupling means being connected tosaid elements at the radially inner ends thereof.

References Cited in the tile of this patent tronics, December 1944,pages 142-145.

Antenna Systems, AF Manual 52-19, 1953, pages 227,

Klass: Airborne Spiral Antennas Minimize Drag, Aviation Week, July 14,1958 pages -82.

